You are exercising your hamstring muscle (the large muscle in the back of the th

Question

You are exercising your hamstring muscle (the large muscle in the back of the thigh). You use an elastic cord attached to a hook on the wall while keeping your leg in a bent position (the figure below).

Part A

Determine the magnitude of the tension force T? HonL exerted by the hamstring muscles on the leg. The cord exerts a 20-lb force F? ConF on the foot.

Part B

Determine the magnitude of compression force F? FonB at the knee joint that the femur exerts on the calf bone.

Explanation / Answer

the net torque = 0

torque = force * lever arm

FConF *(15+1.5) = T HonL * 1.5

THonL = 20*(15+1.5)/1.5 = 220 lb <<<------answer

part(b)

in equilibrium net force = 0

along horizantal

FFonB - THonL + FconF = 0

FFonB = 220 - 20 = 200 lb <<<---answwer

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